Display arrangement



Sept. 15, 1953 A. DAVISON DISPLAY ARRANGEMENT Filed Aug. 18, 1950 lNVENTOR A /an DflV/SON Patented Sept. 15, 1953 UNITED STATES PATENT OFFICE DISPLAY ARRANGEMENT Alan Davison, Liverpool, England, assignor to Automatic Telephone & Electric Company Limited, LiverpooL-En'gland, a British company 8 Glaims.

The present invention relates to display arrangements and is more particularly concerned with the display of variable items of information on the screen of a cathode ray tube.

Display devices of this type find many applications in. the signalling art, one particular application being to number displays used in automatic telephone systems.

It has been proposed in United States Application No. 750,142 to display a plurality of variable characters on the screen of a cathode ray tube by generating varying voltages corresponding to these characters and selecting two or more of them for successive application to the deflecting means of the tube to cause the beam to trace the selected characters-on the screen. The varying Voltages are generated by applying the output of a high frequency generator to a plurality of varying impedances comprising capacitors each having a continuously rotating vane of suitable shape co-operating with a pair of fixed vanes.

The present invention is particularly concerned with display arrangements of the above-mentioned type and has for its object to provide an improved arrangement forv generating the characteristic varying potentials.

According to one feature of the invention in an arrangement for generating varying control voltages suitable for causing, any one or more of a plurality of predetermined characters to be displayed on the screen of acathode ray tube a thermionic tube or tubes of the rotating beam type is or are provided having load impedances associated with individual similar electrodes, the dimensioning of the load impedances being such that the current flow through the load impedances as they are rendered effective succcessively by the rotating beam enables a varying control voltage having a suitable characteristic to be obtained across a common portion of said load impedances.

According to a further feature of the invention in an arrangement for generating pairs of varying control voltages suitable for causing any one or more of a plurality of predetermined characters to be displayed on the screen of a cathode ray tube a pair of varying control voltages is developed across two impedances each connected in the cathode. circuit of separate thermionic tubes of the multi-anode rotating-beam type having an individual impedance of suitable value connected to each anode.

The invention will be better understood from the following description of one method of carrying it into effect which should be read in conjunction with the accompanying drawings, comprising Figs. 1 and 2 in which Fig 1 is a general circuit showing the principal components, and Fig. 2 represents a multi-anode' rotating beam tube of the type used in the generating circuit.

Referring to Fig. 1 the main circuit may be divided into three parts as follows. Part one consists of a layout control circuit which applies appropriate varying voltage successively to one pair of plates of a cathode ray tube and also D. C. layout potentials to another plate of the tube. This equipment may consist of a uniselector LC as shown, having three banks of contacts, LCXI LCX2 and LCY. The contacts of bank LCXI are connected over leads LP to different points of a potentiometer in such away that a difi'erent voltage appears on each contact, the voltages increasing progressively round the bank. The wiper associated with this bank extends a voltage to one of the X plates-of the cathode ray tube and this voltage serves to locate the character in a desired position on the screen. The contacts of the banks LCXZ and LCY are connected to a series of character selecting devices, and correspond to the X and Y components respectively of the characters to be displayed. The wipers associated with thesetwo banks are therefore connected respectively to the second X plate and one of the Y plates of the cathode ray tube, the second Y plate being. connected to earth.

The second part of the circuit comprises the character selecting devices mentioned above. These may also consist of a plurality of uniselectors shown in the drawing as FSI, PS2, etc. As many of these uniselectorsmust beprovided as thereare characters to be displayed simultaneously. Furthermore, each must have two banks FSIX, FSIY etc., and eachbank must have as many contacts asthere are characters available, or alternatively further'uniselectors must-be pro-' vided so that the total number of contacts on all the uniselectors in the character selecting group is equal to twice the product of the number of different characters available and the maximum number of characters it isdesired to display simultaneously. The Wipers corresponding to banks FSIX, FSZX etc;, are-connected to successive contacts of layout control uniselector' LCXZ and those corresponding to-banks FSIY,

FSZY, etc., to successive contacts of uniselector' LCY as shown. The contacts of uniselectors- FSI, FSZ, etc., are multiplied asshown-and con-- nected to a series of sources of varying voltage.

These sources constitute the third part of the circuit and each comprises an electron discharge tube VIX, VIY, etc., of the multi-anode rotating beam type. Each anode is connected to a source of high potential through a, resistor RI, R2, etc., and has in its cathode circuit a resistor RIX, RI Y, etc., connected between cathode and earth. Connections are made to the bank multiples of uniselectors FSI and PS2 from the cathodes of the rotating beam tubes as shown. The values of the anode load resistors RI, R2, etc., are chosen for each tube so that, as the electron beam rotates, the current in each cathode resistor varies to provide the varying voltages required to trace the outline of the desired character on the screen of the cathode ray tube.

The rotating beam tube is shown diagrammatically in Fig. 2 and is of the type disclosed in British Specification No. 539,315 and in the The Bell System Technical Journal Vol. XXIII No, 2 April 1944 pp. 190-202. Only a brief description will be given here. Referring to Fig. 2, the tube consists of a single cathode I surrounded by a plurality of anodes I3, each of which has associated with it an individual grid H and is shielded from adjacent anodes by a screen i2. Outside and surrounding the envelope it of the tube is a stator I5 of laminated mag- .netic material comprising a plurality of polepieces wound as for a polyphase A. C. motor. 'When a polyphase source of current is applied to the winding, a rotating magnetic field is produced which has the effect of focussing the electrons emitted from the cathode into a beam which rotates with the field. Two beams are actually produced in opposite directions, but since only a single beam is required, one is suppressed by applying to the grids successively a potential negative with respect to cathode. This potential may be derived from the polyphase supply and thus the electrostatic field will rotate at the same rate as the magnetic field. The shields between the anodes and the grids not biased to suppress the unwanted beam may be maintained at cathode potential and serve to suppress secondary emission from the anodes. It will be seen that the grids may be connected in groups since the biasing potential may be applied to more than one grid simultaneously provided the group does not include the grid associated with the conducting anode. An alternative arrangement in which the need for a stator is obviated employs a rotating electrostatic field only. The grid associated with the conducting anode is raised to a positive potential while the remainder of the grids are biassed negatively with respect to cathode.

The principle of applying two varying potentials to a cathode ray tube to cause the beam to trace a character on the screen has been described in United States Application No. 750,142. The beam is preferably deflected to trace the character and then to retrace it in the opposite direction. ihis eliminates fiy-back after each cycle and the consequent complications which would be required to black out that portion of the trace. The required voltages may be determined as follows. The characters are first drawn on a pair of axes representing the deflection caused by the X plates and Y plates respectively, and then divided into a number of equal divisions representing fractions of the cycle. The number of divisions should be equal to half the number of anodes in the rotating beam tubes since each figure is traced twice in each cycle, a suitable number of anodes being 20 per tube. The X and Y co-ordinates of the centre point of each of the divisions may then be taken to represent the potentials which must be successively applied to the plates of the cathode ray tube to trace out the character, since the deflection is substantially proportional to the applied potential.

The varying potentials are obtained from the voltages developed across resistors RIX, RIY, etc. As the beam rotates, the current in the cathode resistor varies, due to the rapid changes in anode load, and a capacitor CIX, CIY, etc., may be shunted across the cathode resistor to smooth out the changes in voltage so that a smoother trace is obtained on the cathode ray tube. All the rotating beam tubes are in operation simultaneously and the varying potentials generated appear continuously on the contacts of the character selecting uniselectors FS. The characters which are displayed on the screen of the tube are determined by the positions of the wipers of uniselectors PS I, F82, etc., which would, for example, be set by impulses from equipment external to that described. The wipers of layout control uniselector LC rotate at a constant rate over as many of its contacts as are being used for the display. The X and Y wipers apply to the appropriate plates of the cathode ray tube the two components of each character in turn. It will be seen that if more'than one line of characters is to be displayed, a fourth bank of the uniselector FS could be used to apply locating potentials to the second Y plate instead of earth potential, in the same way as the wiper associated with bank LCXI applies locating potentials to the second X plate.

The beam of electrons in a multi-anode tube can be made to revolve at a much greater rate than a corresponding mechanical device, and hence an apparently simultaneous display of a greater number of characters could be obtained without flicker on the screen, which would preferably be of the slow type, than with a mechanical device.

The foregoing description relates to one embodiment of the invention and it will be appreciated that modifications could be made in the arrangements described without departing from the spirit and scope of the invention. For instance, instead of using the voltage developed across the cathode resistors, the voltage developed across anode resistors could be employed. In this case each anode would have an individual resistor all of which would be connected in parallel on the H.T. side and would be connected to the HT. supply through a common output resistor. Again one or more thermionic tubes of the rotating beam type having a plurality of sets of anodes could be used to reduce the number of tubes required. In this case a single stator could replace several used for individual tubes, and the output voltages would be developed across output resistors common to a set of anodes and disposed between the HT. supply and the junction point of the load resistors. Alternatively the generating tubes could be of the type having a plurality of cathodes and a single anode. Again, the uniselectors could be replaced by an arrangement of relays or other switching devices.

The invention provides an adaptable display device which has many applications in the signalling art. It is capable of displaying characters separately or in groups, and the characters may equally well be letters, figures or a combination of the two.

I claim:

1. Apparatus for generating varying control voltages suitable for application to the deflecting means of a cathode ray tube to cause any number of a plurality of characters to be displayed on the screen thereof comprising at least one pair of thermionic tubes of the rotating beam type each having a plurality of individual similar electrodes, and individual load impedances connected to each individual electrode, a common load impedance for each tube connected in circuit with the individual load impedances for said tube, the dimensioning of said individual load impedances being such that the current flow through said individual load impedances as they are rendered eifective successively by the rotating beam enables a varying control voltage to be obtained from each of said common load impedances and means for applying said varying control voltages to said deflecting means.

2. Apparatus as claimed in claim 1 wherein each of said individual similar electrodes are anodes and including a single cathode in each of said tubes, the individual load impedances comprising a resistor connected to each of said anodes while the common load impedance comprises a common cathode resistor.

3. Apparatus as claimed in claim 1 wherein each of said thermionic tubes includes a plurality of sets of anodes comprised of the individual similar electrodes and wherein each tube has a single cathode for each of said sets of anodes.

4. Apparatus as claimed in claim 1 wherein the individual similar electrodes of each of said thermionic tubes comprise a plurality of cathodes and wherein each of said tubes has a single anode, the individual load impedances comprising a resistor connected to each of said cathodes while the common load impedance comprises a common anode resistor.

5. Apparatus for generating varying control voltages suitable for application to the deflecting means of a cathode ray tube to cause any number of a plurality of characters to be displayed on the screen thereof comprising a plurality of pairs of thermionic tubes of the rotating beam type, each tube having a plurality of anodes and a single cathode, an individual load impedance connected to each anode, a common load impedance connected to said cathode, the dimensioning of said individual load impedances being such that the current flow through said individual load impedances as they are rendered effective successively by the rotating beam enables a varying control voltage to be obtained from each common load impedance, a plurality of uniselectors each having a pair of wipers and associated bank contacts, connections between the bank contacts associated with one wiper of each of said uniselectors and the common impedance of a tube of each of said plurality of pairs of tubes and between the bank contacts associated with the other wiper of each of said uniselectors and the common impedance of the other tube of each of said plurality of pairs of tubes and means for connecting said wipers to said deflecting means.

6. The apparatus claimed in claim 5 including a further wiper and associated bank contacts connected between a source of direct potential and said deflecting means whereby movement of said wiper over said contacts adds selected direct potentials to the deflecting means in conjunction with varying control voltage applied thereto by at least one of said uniselectors.

7. Apparatus for generating a multiplicity of varying control voltages comprising at least one pair of rotating beam type electron tubes each having a plurality of similar electrodes respectively electrically insulated and an individual electrode adapted successively to be in electrical connection with said similar electrodes through the medium of the rotating beam, a source of supply for said tubes, individual impedances respectively disposed between said source and said similar electrodes, a common impedance for each of said tubes connected between the individual electrode thereof and said source, and interconnected switching means in electrical connection with said common impedances for selecting varying control voltages developed thereacross in accordance with the instantaneous position of the rotating beam.

8. The structure as claimed in claim 7 wherein said interconnected switching means comprise a plurality of uniselectors each having a pair of wipers and associated bank contacts, connections between the bank contacts associated with one wiper of each of said uniselectors and the common impedance of one of said tubes and between the bank contacts associated with the other wiper of each of said uniselectors and the common impedance of the other of said tubes and including a further wiper and associated bank contacts connected to select successively potentials of different magnitude and add the selected potentials to said varying control voltages.

ALAN DAVISON.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,114,613 Schlesinger Apr. 9, 1938 2,214,729 Hickok Sept. 17, 1940 2,247,350 Colberg July 1, 1941 2,302,311 Goldsmith Nov. 17, 1942 2,365,476 Knoop et a1 Dec. 19, 1944 2,395,299 .Skellett Feb. 19, 1946 2,512,655 Kohler June 27, 1950 2,513,947 Levy July 4, 1950 2,522,055 OBrien Sept. 12, 1950 2,533,401 Schramm Dec. 12, 1950 2,534,372 Ring Dec. 19, 1950 2,573,175 Bergen et al. Oct. 30, 1951 

